QUESTION: When a horse ships long distances to race, why do some lose so much weight…and how long does it take them to recover fully?

DR. PETER MORRESEY: Transportation causes stress in horses. Many things are done to minimize this, but stress cannot be eliminated completely and like people, horses respond individually. Many studies have been performed to assess metabolic and physical changes in transported horses.

During transport, heart and respiratory rates increase. The stress hormone cortisol is released, promoting breakdown of body tissue and energy stores. The levels of other hormones involved in metabolism (e.g. thyroid hormone) are also altered.

Transportation also results in the horse constantly needing to preserve balance, requiring energy from his muscles. This is most needed during acceleration and deceleration of the transport vehicle, so the skill of the driver also affects body condition.

All of these alterations to the daily needs of the horse over and above maintenance consume energy. In addition to this, exposure to new horses and novel environments provide an infectious challenge; this, too, has an energy cost to defend against.

During transportation, horses vary in their water and food intake. If the horse eats and drinks adequately, losses will be comparatively small and easily made up. When the horse cannot or will not eat enough due to circumstance or personality, these reductions compound the loss of energy stores and body condition (muscle, fat).

Recovery time varies between individuals. Time taken to recoup losses depends upon the ability of the horse to resume intake adequate to replace losses and meet ongoing needs. For some horses this is not difficult and they rapidly adjust with minimal outward signs. For others, situations of stress resulting from a new environment, altered social setting, and variations in the food offered due to different hay/concentrates and water source (which can greatly affect taste) mean many days may be needed to regain body condition and energy stores depleted on their journey. There is no set period over which this may occur. Special attention should be paid in the days following transportation to the vital signs of the horse, with alterations in respiratory rate or effort, or elevations in rectal temperature, requiring prompt veterinary attention.

Opportunities to ease the stress and resulting losses due to transportation include acclimating the horse to trailers or stalls well in advance of the time of transport, progressively altering food offered to match that available during their journey, and ensuring in the initial period after arrival that routine and feedstuffs to as great of a degree as possible do not deviate any more than necessary from that which the horse might expect.

Dr. Morresey began his career in New Zealand as a mixed animal practitioner following graduation from Massey University in 1988. He completed a theriogenology residence at the University of Florida and spent time as part of clinical faculty at the University of Pennsylvania. Areas of interest include reproduction, internal medicine, neonatal medicine, veterinary business and Chinese medicine.

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